// Numbas version: finer_feedback_settings {"name": "Simon's copy of SFY0004 Implicit 1", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"parts": [{"extendBaseMarkingAlgorithm": true, "showFeedbackIcon": true, "showCorrectAnswer": true, "scripts": {}, "sortAnswers": false, "stepsPenalty": 0, "marks": 0, "unitTests": [], "prompt": "\n

Using implicit differentiation find $\\displaystyle \\frac{dy}{dx}$ in terms of $x$ and $y$.

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Input your answer here:

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$\\displaystyle \\frac{dy}{dx}= $ [[0]]

\n \n \n ", "variableReplacementStrategy": "originalfirst", "steps": [{"prompt": "

To differentiate implictly, we must differentiate both sides of the equation with respect to $x$

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Notice (from the chain rule) that  $\\frac{d}{dx}f(y) = \\frac{df}{dy}\\frac{dy}{dx}$

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Hence, for example  $\\frac{d}{dx}y^2 = \\frac{d}{dy}(y^2)\\frac{dy}{dx}=2y\\frac{dy}{dx}$

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Implicit differentiation.

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Given $x^2+y^2+ax+by=c$ find $\\displaystyle \\frac{dy}{dx}$ in terms of $x$ and $y$.

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Given the following relation between $x$ and $y$
\\[\\simplify[all,!collectNumbers]{x^2+y^2+{a}x+{b}y}=\\var{c}\\]
answer the following question.

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To differentiate implictly, we must differentiate both sides of the equation with respect to $x$

\n

Notice (from the chain rule) that  $\\frac{d}{dx}f(y) = \\frac{df}{dy}\\frac{dy}{dx}$

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Hence, for example  $\\frac{d}{dx}y^2 = \\frac{d}{dy}(y^2)\\frac{dy}{dx}=2y\\frac{dy}{dx}$

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(a)

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On differentiating both sides of the equation implicitly we get
\\[2x + \\simplify[all,!collectNumbers]{2y*Diff(y,x,1) + {a} + {b} *Diff(y,x,1)} = 0\\]
Collecting terms in $\\displaystyle\\frac{dy}{dx}$ and rearranging the equation we get
\\[(\\var{b} + 2y) \\frac{dy}{dx} = \\simplify[all,!collectNumbers]{{ -a} -2x}\\] and hence on further rearranging:
\\[\\frac{dy}{dx} = \\simplify[all,!collectNumbers]{({ - a} - 2 * x) / ({b} + (2 * y))}\\]

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